This invention relates to optical recording mediums and, more particularly, to an optical recording medium comprising a recording layer, having a characteristic of forming small halls called pits with a recording light such as laser beam.
Ordinarily, optical recording mediums have superior characteristics, such that they have a large storage capacity and are capable of effecting writing or reading in a non-contact manner. Optical recording mediums have therefore been developed extensively.
A write once type optical disk is known as an example of optical recording mediums. This type of optical disk is used in such a manner that a laser beam is condensed to a very small area on a recording layer and is converted into thermal energy to change the state of the recording layer (forming pits) thereby to write data, and that the corresponding data is reproduced in accordance with changes in the quantity of light reflected on recording portions and non-recording portions.
Preferably, the recording layer of such a medium is formed of a material capable of achieving a large change in reflectivity. Further, it is necessary to use non-toxic material for forming the recording layer, to improve the sensitivity of medium and to reduce the manufacture cost. Therefore, optical recording mediums having a recording layer formed of an organic material mainly constituted by a coloring matter have been proposed. However, a conventional recording material is not sufficiently available, because there are many cases where pits in the recording layer formed with irradiation of laser beam are out of shape. That is, as an end portion of the pit is formed of fused and flowed recording material, the pit is in the shape of so-called ellipticity having a tail. Therefore, a so-called "hump phenomenon" is observed in a reproduction waveform. In result, it is difficult to have superior reproduction characteristics.